Specimen test slides and procedures for detecting occult blood in fecal matter are well known. For example, U.S Pat. No. 3,996,006 discloses slides having a specimen receiving sheet between a front panel and a rear panel with openings in the front and rear panels and pivotal covers or flaps to cover these openings. One such test slide is sold under the trademark of `Hemoccult`.
The specimen receiving sheet is generally an absorbent paper impregnated with a guaiac reagent. The hemoglobin catalyzed oxidation of the guaiac extract coated paper is used clinically to detect occult blood in feces. Briefly, the test procedure is as follows.
A sample of fecal matter is smeared onto the guaiac paper through an opening of the front panel. The panel is then covered and the flap of the rear panel is opened. A developing solution such as hydrogen peroxide is applied to the guaiac paper via the corresponding opening in the rear panel. If blood is present in the fecal matter, the guaiac reaction will color the paper blue. The overall reaction is a follows: ##STR1##
One of the problems associated with this test is the number of false negatives, i.e., negative test results in samples of known bleeding patients. The test is not sensitive enough to pick up lower levels of blood in the feces.
Another disadvantage of the guaiac test is that other non hemoglobin type compounds present in the stool, such as peroxidases present in certain foods, will also catalyze the oxidation of guaiac and result in a blue color. This results in false positive reaction, i.e., a positive reaction without fecal occult blood present.
Previous attempts have been made to increase the sensitivity of the present Hemoccult.RTM. test. Hydration of the smear prior to development is often employed. However, while hydration produces a more sensitive test the method also adversely affects the specificity of the test. It produces unacceptable high false positive rates by reacting with other interfering substances such as vegetable peroxidases.
It is therefore the object of this invention to increase the sensitivity of the test while improving or maintaining the specificity of the current Hemoccult.RTM. test. Increasing the sensitivity includes detecting lower levels of blood in the feces and obtaining greater readability, i.e., obtaining a clearer and deeper blue color with the same concentrations.
Briefly, this invention consists of an improved developing solution for determining fecal occult blood in a sample using a test matrix containing guaiac. The solution comprises an alcoholic solution of hydrogen peroxide and certain enhancing agents. The developer is largely alcoholic, containing a minimum amount of water. It was unexpectedly discovered that when these enhancing agents were added to the developing solution a more intense and readable blue color end point resulted than obtained in the current fecal occult blood tests. Further, the novel solution of this invention degrades and inhibits the more labile peroxidases which also catalyze the oxidation and produce the same color change.
The enhancers employed in this invention comprise phenolic type compounds. Examples of such enhancers are esters of hydroxybenzoic acid such as methyl, ethyl, propyl, butyl, benzyl, and phenyl parahydroxybenzoates. Preferably the lower alkyl esters of p hydroxybenzoic acid having from 1 to 4 carbon atoms, also known as parabens, are employed in this invention. Other examples of enhancers are phenol, guaiacol, p hydroxybenzoic acid, 3,5-dimethylphenol, methyl salicylate, 3,5 dichlorophenol, p-nitrophenol, p-bromophenol. The enhancer is present in an amount of from about 0.4% to about 20% by weight of the developer solution. Preferably the enhancer is present from about 1% to about 10% by weight of the developer.
The developing solution is largely alcoholic. The alcohol employed may be any of the lower alkanols, i.e., containing one to four carbon atoms. The alcohol will be present in an amount of from 60% to about 90% by weight of the developer, preferably from about 70% to about 90%. Advantageously, ethanol is the alcohol employed.
The stabilized hydrogen peroxide will be present from about 1% to about 10% by weight, preferably from about 3% to about 6% by weight of the developing solution.
Water will be present from about 7% to about 23% by weight, preferably from about 7% to about 14% by weight of the developing solution.
Tests were conducted to demonstrate the advantages of the novel developing solution of this invention over the conventional developer employed in the fecal occult blood tests. These tests were performed by spiking fecal samples with various concentrations of blood. Whole blood in the amounts of 0, 0.2, 0.5 and 1 ml of blood were added to 100 gm of feces. Horseradish peroxidase was also added to fecal samples for this study. The color rating scale employed was as follows.
______________________________________ SCALE DESCRIPTION ______________________________________ - No blue color. + Very faint, barely detectable (trace) blue. Blue color fades rapidly and disappears within one minute. ++ Faint blue color after development. +++ Distinctly blue color. ++++ Intense blue color. Wider area of blue color coverage. ______________________________________